Sharpening, shaping and finishing of electrically conductive materials



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INVENTORJ CHARLES L. FAUSTM P BY JOHN ECLIFFOBD.

' OBA/E7-5 United States Patent SHARPENING, SHAPING AND FINISHING OF :1 1 ELECTRICALLY CONDUCTIVE MATERIALS Charles L. Faust and John E. Clifford, Columbus, Ohio,

assignors, by mesue assignments, to The'Cleveland- Twist Drill Company, Cleveland, Ohio, a corporation )f Ohio Filed A r. 9, 1956, Ser. No. 577,015 12 Claims. Cl. 204-142 charge processes that erode away a metal surface by are orspark discharge from the metal to another electrode in a di-electric medium; electrolytic process in which the metal item to be ground is made anodic in contact with diamonds or other non-metallic abrasive on a metal cathode or in contact with a metal as cathode; and sonic or ultrasonic processes that cut by high frequency vibration of a metal with abrasive powder between it and the material to be cut.

All the above-mentioned non-mechanical processes have advantages and limitations. The electric discharge, sonic and ultrasonic methods are especially adapted to drilling small holes or forming small cavities in materials hard to pierce, drill or form by conventional methods of piercing with twist drills or for forming cavities with routers, reamers, etc. These methods have been explored for shaping and finishing, and are meeting with some industrial successes, but their limitations prevent them from fully meeting the extensive needs cor grinding and shaping hard-to-grind materials that now can be cut or ground only by diamond wheels or cannot be cut without damage with abrasive wheels of any type now known.

Certain of the electric discharge processes, for example, operate at 25 volts or higher, cut at practical speeds that cause rough surfaces; or produce smooth surfaces at impractically slow cutting speeds; do not produce sharp edges at reasonable rates of metal removal; and have best application for drilling or producing cavities. Sonic and ultrasonic methods have found very limited uses other than in drilling and in forming of cavities. For the electric discharge, sonic and ultrasonic methods, the electrode disc or drilling tool wears away at a rate almost the same as that at which the work piece is cut away by the electrogrinding or the drilling action or the cavity forming action. The attritional action on the important part of the machine adds to the cost through need for replacement because of change in contour and/or wearing away of the cutter, and for shut-down time to make such changes.

The so-called electrolytic grinding process requires the use of a diamond (or other inert non-metallic, non-conducting abrasive or metal) in contact with the work made anodic in an electrolytically conducting, but substantially neutral solution, such as a solution of sodium silicate, or of sodium nitrate and sodium nitrite in water. The prior art teaches the need for diamond (or other 2,939,825 Patented June 7, 1960 abrasive) wheels or discs for two major reasons: (1) the protruding diamonds act as spacers touching the surface of the article to be finished so as to automatically maintain spacing that fixes the thickness of electrolyte film; and (2) to scrape away from the surface the insoluble salts or oxides that form on and adhere to the surface of the article being finished. Bythese two requirements, the prior art limits the cutting rate (rate of metal removal) because: the non-conducting diamonds reduce the active cathode area and the maximum current is limited to correspond to a lower anode current density than if the diamonds wereabsent and the conducting area were increased by the amount of area occupied by the diamonds; the diamonds further decrease the maximum operating current by restricting electrolyte flow over the cathode surface so there is polarization in the electrolytefilled valleys and electrolysis current flow is limited; or the metal-removal rate is limited to the current flow that formssolid adhering anode products at a rate just equal to that at which the products are scraped away by the diamonds.

The present invention has shown that cutting or metalremoval rates by anodic electrolysis can greatly exceed those reached by the aforementioned non-mechanical methods, without mechanical action by or physical contact with the article being electrolytically ground or machineda This is electrolytic grinding in its true coulombic meaning without mechanical contact and/ or action. Consequently, sur-faces are smooth, no stresses of any kind are induced into the surface of the article being shaped or finished, and hardness or composition of the metal or electrically conducting material has no significance, and volt-ages are 25 volts or less and are usually 4 to 8 volts, which are so low as to bewithout danger to machine operators. As is described hereinafter, it has been shown that metals and electrically conducting materials can be electrolytically ground at speeds at least twice those at which diamond wheels can grind such materials as cemented tungsten carbide; i.e., up to 0.05 inch per minute; and vanadium tool steels at speeds up to 0.14 inch per minute, metal removal depth. This latter speed and more can be attained for mild steel, tool steels, etc., and non-ferrous metals and alloys, without Wear on the cathode or cuttingdisc which is inexpensive but is properly designed as-to form. This feature of no wear is immediately recognized as a significant fact for automation in shaping operations with contour wheels, for example, as well as for fiat surface shaping, sharpening and finishing. Savings in operating costs accrue from long runs without costly down time for re-dressing wheels or for ultimately replacing them.

It is a primary object of this invention, therefore, to provide methods and apparatus for electrolytically grinding metals and other electrically conducting materials without mechanical action or physical contact of any kind.

It is a further object of this invention to provide methods of and apparatus for shaping, sharpening and finishing metals and electrically conducting materials without generation of damaging heat, introduction of stresses from pressure, mechanical work, or electric discharge.

It is still a further object of this invention to provide methods of and apparatus for the simultaneous grinding of combinations of metals presenting very hard and relatively soft metals to the grinding operation; for example, cemented tungsten carbide inserts, silver solder, and tool steel.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments ofthe invention, these being indicative, however, of but a few of the various ways in whichthe principle of the invention may be employed.

This invention may be broadly defined as the method of electrochemically eroding the surface of an electrically conductive body which comprises:

(a) Providing an electrolyte in which said body is electrolytically soluble;

(b) Relatively moving said body, as an anode, sub stantially in surface contact with a continuouslayer of said electrolyte, which 'is supported on a cathode which is in spaced relation to said anode;

While maintaining a direct current said body and electrolyte;

(d) Said method characterized further in that said anode and cathode are at all times in physical spaced relation. v

By the term electrolytic dissolution as used throughout this description and in the claims is meant the substantial complete dissolution progressively of the surface of a material according to Faradays law. When metals orjelectrically conductingmaterials are made anodic in electrolytic solutions in such conventional processes as electroplating and electropolishing, dissolution rate depends on the current density that can be maintained without polarization of the anode or the cathode. I Polarization increases resistance to flow of electric current so. that electrolysis current decreases and dissolutionrate falls oif, )1;a hlgh1 applied voltage is required; For any electrolyte, there is a maximum voltage above which further increase will not cause the required electric current flow for a given metal anode and indeed may even cause current'to cease to flow because of the formation of an insoluble film of oxide or salt on the metal "anode surface. 7 Because of polarization, dissolution rates of anodes are slow relativeto the metal removal rate needed for practical grinding and shaping of metals in machine shop practices. By electrolysis as in plating, electroetching, or electropolishing, metal dissolution rates do not exceed 0.05to 0.1 inch per hour. Other i'nvestigators have increased electrolytic dissolution by rneans ofmechanical assistance given by electrically conducting abrasive wheels in contact with the article being electrolytically ground so as to continuously scrape away insulatingsalt or oxide coatings, and thereby, provide for continuousv high-current density anodic dissolution. For example, Keeleric, and others using his process, using neutral solutionsof sodium salts in water, passed direct current through cemented tungsten carbide and achievedsubstantial metal removal rates but only because of scraping action of an electrically conducting diamond grinding wheel touching the surface of the cemented carbide. .Thus, Keeleric effected a significant improvement in anodic dissolution for grinding and shaping. But, the Keeleric method, as do others known as electrolytic grinding, depends on physical contact and scraping or even actual abrasive cutting simultaneously and'requires costly diamond wheels which are electrically conductive and of specialdesign. Any process which depends upon physical contact or abrasive cutting may result inadamaging heatingof thework. Furthermore, efiectiveness of such a process depending on scraping and/or abrasive cutting is limited in maximum cutting flow. between 'rateto those conditions of relative rate of film formation 'and removal by'scrap'ing,

V Asignificant and greater increase in' electrolytic grindrate would be attained if solid film formation was "avoided and the need for lscraping or physicalcontact with abrasive or rubbing surface accordingly eliminated.

By the method ofthe present invention such an accomphshment is'realized by very accurate control of thefiim thickness of electrolyte supplied at very high fiow i'ate across the surface of a metal as an anode to be ground or shaped. By this method commercially practical grinding or cutting rates of metal-removal are accomplished without spark or are discharge. The dissolution is strictly electrolytic in the coulombic meaning.

By the use of the method of the present invention, cemented tungsten "carbide, has been cut at a tuetal remova l ra'te of-0:057 inch per minute at 1550 aifip'ereis per square inch at 76 percent anodic current eificiency, or'of 0.040 inch per minuteat .perccntanode efiiciency.

It isv not unexpected that technical and .patent literature described processes in which scraping or abrasive assistance is required for electrolytically grinding cemented tungsten carbide. Most usually, the cementing metal is cobalt. Tungsten oxide is Well-known to be soluble in alkaline solutions and insoluble in acid solutions. Cobalt oxide isinsoluble in alkaline and soluble in acid solutions. Oxides of both metals are insoluble in neutral solutions. Polarization causes metal oxide films to form on anodes when limiting current densities are exceeded. Limiting current densities are much too low for tungsten carbide cemented with cobalt in simple acid, neutral or alkaline solutions for practical electrolytic grinding rates without scraping to remove either tungsten oxide or cobalt oxide, dependingon whether the electrolyte is acid or alkaline. When utilizing methods which depend on scraping of the anode face, the disadvantage exists in that control is difficult and critical for .niaintaining light wheel contact, yet avoiding .pressure that introduces cutting by the abrasive and, thus, wheel was; as well as a damaging heating of the work.

By "the method of the present invention cobalt cemented tungsten carbide can be electrolytically ground or cut at high metal-removal rate without abrasive wheel or other wheel contact by using an alkaline electrolyte in which tungsten oxide is very soluble and which contains 'a s'olubilizirig anion for rendering ccbalt'very soluble. A suitable electrolyte contains sodium tartrate, sodium hydroxide and sodium chloride.

, Providing an electrolyte with capacity to accept tung- "sten 'and cobalt at high rates by anodic dissolution of cementedtungsten carbide is not alone sufi'icient for highspeedelectrolytic grinding. The electrolyte must be replaced at a high rate at the'anode face. Such replace- :ment canfbe effected in 'a satisfactory manner by distributing the electrolyte in a layer less than 0.020 inch andusu'all'y less than 0.008 inch in thickness on a rotating cathode disc as hereinafter described.

Apparatus for carrying "out the novel method of the prese t invention is illustrated in'the drawings.

In the annexed drawings:

Fig.1 isa"prspectiveview'of'one form of apparatus which'may be used in carrying out the process of my fiv b' Fig.2 is aperspective View"partially in section and 'jdri'awn"t'o'an enlarged scaleofa'portion of the apparatus rnustrarea i'nFig. 1 showing in greater detail the cathode disc on which the electrolyte is supported and to which is' presented the body to be electrolytically ground;

Fig, 3 is an enlarged'fragmentary'view of aportion "of the assemblage illustrated 'in Fig. 2 showing in. greater particularity the physical relationship between the cathode, a gae and the electrolyte film therebetween;

Fig. 4 'is an illustration of an alternative form of apparatus by which the" method of this invention may be ar dfd 'Fig."5 is a' graph showing the eliect of anode-to;cathode spacing on the current density and-cutting rate whenthe method "or this invention is 'used for electrolytically grinding cementedtungsten carbide; v jFig. 6 isa sin'lilargraph' when the object electrolytically g rofind ishiade of high vanadium steel; 7 a

Fig. 7 isa' diagrammatic'representation of onemethod "ofconti'dlliiig 'the'spac'ing between the anodic work piece and th'cathde.

Fig. 8 is a graph showing the general relationship between current density, cutting rate and spacing between the anode and cathode at various voltages;

Fig. 9 is a diagrammatic representation of another method of controlling the spacing between the anodic work piece and the cathode; and

Fig. 10 shows a list of schematic wave-form diagrams illustrating phase relationship associated with the fun tioning of the gap control system of Fig. 9.

Fig. 1 is a drawing of a machinefor electrolytic grinding employing a cathode disc rotatable in a horizontal plane. The cathode disc is affixed to a rigid electrically insulated spindle driven by a suitablypowered motor,

preferably having variable speed so that the spindle can be rotated at speeds up to 10,000 rpm. or more. A universal vise is mounted in position so that the part to be ground and held thereby can be advanced toward or retracted from the surface of the disc and can be moved in a direction parallel with a radius of the disc and in addition can be moved in a direction substantially parallel with the plane of the disc. The machine is also provided with a liquid circulating system for introducing the electrolyte to the surface of the disc and forcollect ing the overflow so it can be kept in continuous circulation by means of a suitable pump. The machine has a hood enclosing the grinding area in a manner that enables the operator to observe the operations. Having thus described in general terms the principal components of the machine and their respective functions, the following description will now identify, in detail, by appropriate reference characters, the various elements of the machine as illustrated in Figs. 1, 2 and 3., V 1 is the spindle on which the cathode disc 2 is carried. 3 is the system for circulating the electrolyte and it comprises a pump 4, adelivery conduit 5 which is terminally provided witha dam 6 held in a predetermined spaced relation with the upper acting face of the cathode disc 2.

While in the preferred embodiment of the invention appropriate means may be provided for the purpose of regulating the gap between the lower edge of the dam and the upper surface of the cathode disc, such adjusting means have been omitted from Fig. 1 for purposesof clarity in the drawing.

The housing 7 has its bottom 8 arranged to slope centrally to a discharge opening 9 which is covered by a bafiie plate 10 in spaced relation to the bottom in which the discharge opening is formed. The discharge opening has a return conduit 11 connected therewith, by which the electrolyte is fed back to the pump 4. If desired, a drain connection generally indicated at 12 may be provided in the return conduit 11 for the purpose of draining the electrolyte from the system. Suitable means may be provided such as a float in the tank or housing for the purpose of maintaining a proper level of elec- ,trolyte, i.e., supply of electrolyte in the system.

The electrical panel 13 contains the ampere-minute meter, ammeter and rheostat necessary for adjusting and maintaining the operation by automatic means based on voltage control as hereafter more fully explained.

Spindle 1 extends upwardly from the cathode disc into a drive housing 14 where it.is rotatably supported for high-speed operation. In view of the close tolerances necessary to be maintained between the work which is .anodic and the active face of the cathode disc, it is essential that the spindle 1 be so supported that it will not wobble during operation. In the illustrated embodiment of the apparatus, the spindle is driven by means of a ,"remotely mounted motor 15 through a flexible belt 16.

; per minuteof the spindle may be indicated.

Referring now more specifically to Fig. 2 it V noted that the Work piece or anode indicated at 18 is actually a hard metal alloy insert in a drill, the body of which, indicated at 19, is at its opposite end held in a universal vise generally indicated at 20, although any other suitable means may be employed for adjustably supporting the anode in any desiredposition with respect to the upper surface of the cathode disc 2. The external controls generally indicated at 21 by which the universal vise is adjusted are as illustrated in Fig. 1 conventional, but these may vary also as referred to above.

In order to insure proper circuit characteristics for the electrochemical grinding circuiting, the spindle 1 at its lower end below the disc 2 is provided with aprojection generally indicated at 22 which dips into and rotates in a mercury bath contained in cup 23 from which extends a conductor member 24 which terminally carries a lead 25 which will be connected in the same circuit as the lead 26 on the visemember 20. The cathode disc 2 may have any desired physical dimensions as for example in the machines which have been operated successfully thus far, the cathode disc has had diameters of 8 and 12 inches respectively. The only diflerence which exists when using discs of different diameters is that correspondingly different spindle speeds are necessary in order to maintain the same surface speed on that area of the disc with which the work is adjacent. The upper surface of the disc may be planar, but preferably it is slightly conical. Preferably, it is the surface of a very flat right cone. When a conical surface is thus used the elements of the cone should slope upwardly at an angle of about 1. For certain purposes such as when employing an electrolyte of certain viscosity or when forming a surface on the work which is other than fiat, that is, contour grinding or for a variety of other reasons, the shape of the upper surface of the cathode may vary from that of a right cone.

It is essential for most purposes that the electrolyte supporting surface of the cathode be as smooth as practical in order that the film may be distributed thereover with a turbulence.

Since the path of the electrolyte film issuing from beneath the dam 6 is a resultant of its circumferential and radial progression, for certain types of operations it is desirable to orient in a particular way the surface of the work piece contacting the electrolyte film. Thus, it has been found that when operating at the higher voltages such as in the vicinity of 25 volts, and if a sharp cutting egde is desired, the work should be oriented so that such edge occurs on that side of the tool facing upstream and that the line representing the cutting edge be substantially at right angles to the direction of relative movement between the film and work piece.

The present method is characterized by the employment of current densities considerably higher than the prior art processes referred to previously. For the purpose of maintaining such current density different voltage levels are required depending on the thickness and other characteristics of the electrolyte film. When utilizing electrolytes of the character referred to herein, it has been found that for the purpose of utilizing 25 volts, the electrolyte film has a thickness such that whereas there is substantially no turbulence in the area where the film meets the work and that edge is accordingly made sharp, in the area where the film leaves the work thereis sutficient turbulenceso that the edge is less sharp.

When, however, the film thickness is reduced soas to require only 5 volts for the same current density, the film becomes so thin that the turbulence thereof is verysubstantially reduced and under such conditions of operation the leading edge of the work is made even more sharp than when utilizing a thicker film and a higher voltage and the trailing edge of the work, at the lower voltage level conditions of operation, is also relatively sharp, that is, the trailing edge of the work IIQQF: J5

volt operative conditions has been found to be'sharper ihan the leading 'edgeunder 25 volt operative conditions The factors just discussed signify the essential .dilicr- 'ence between the present process and the processes of the prior art, for example, those "wherein the cathode carries projections which extend into or through the film in substantial contact "with the work for the purpose of for example, removing from the work surfaces the films form'edthereon by the electrochemical action.

In view of the factathat the cutting speeds which can be achieved by the use of this'methodiare substantial, and the further fact that for best operations, the space between the cathode and anode are relatively smalhit becomes important :to provide :some means for adjusting such spacing. ".It liS possible to effect such adjustment manually by means of .thecontrols illustrated, for exampic, at 21in Fig. .1 for the reason that under .fixed operating conditions a definite'relationship exists between the current density, cutting :rate and gap distance. The an- :ode feed rate is the independent variable which determines the gap distance, current density and cutting rate. At equilibrium grinding conditions, the cutting rate is equal to the anode feed rate and the current density and gap distance have fixed values. If the anode-feed rate is increased'slightly above the cutting rate, the gap decreases, the current density increases, and the cutting rate increases until it equals the increased anode-feed rate. Whenequilibrium conditions have been re-established at the higher anode-feed rate, the gap is smaller and the current density is higher. If the anode-feed rate is. decreased slightly below the cutting rate, the gap increases, the current density decreases and the cutting rate decreases until it equals the reduced anode-feed rate. When equilibrium conditions have thus been re-established at the lower anode-feed rate, the gap is larger and the current density is smaller. The above examples show that once the anode-feed rate is set, the electrolytic process is inherently self-correcting. It is thus possible 'to operate thepresent method by controlling the feed rate manually after some experience has been had along .this line. The self-correcting tendency just explained will tolerate rates of feed which, when controlled manually, are either not at the maximum or are of a varying nature within limits. For most consistent results, however, it is desirable that some means he provided which are functionally responsive to one of the variables re- .f erred to and which will automatically maintain afeed rate which bears a predetermined proportional relation .to such variable. For example, since the thickness of the film or, more accurately the space between the anode and cathode when varied is reflected in. substantial changes in current values at a uniform voltage, means, presently to bev described in greater detail, which are functionally "responsive to variations in current can be used for the .purpose of maintaining the feed at a constant rate.

Simply pouring the electrolyte at the not-quite touching conjunction of the rotating disc cathode and the article being ground, as is done by pumping the'oil-emulsion coolant and lubricant out of a tube so a stream strikes the grinding wheel where it touches the article being ,ground in conventional abrasive wheel grinding machines and-1n electrolytically assisted grinding wheels described in the..literature,iis not suitable for electrolytic grinding whenperforming the method of the present invention.

In the machineshown. in Fig. 1, a thin coating of electrolyte is metered onto the disc surface by a deflecting dam. The clearanceof the. dam above the-disc and the rotational speed of the disc are such that the electrolyte is firmly impacted against the disc by centrifugal force until after it has passed under the article being elec- "trolyticallyfground' or out. This .force is believed to so condition thefilm of electrolyte on the disc that substantially no turbulence occurs in the electrolyte film as it passes through the gap'between the disc and the article ibei'ngground. Such absence of turbulence is believed degree bevel at the outer edge.

confirmed by the fact that flat surfaces without waviness and with sharp edges result from theanodic dissolution that efiects anodic grinding. Turbulence, if present in the electrolyte film, would be accompanied by waviness or flow patterns formed in the ground surface. Fig; 1 shows the disc in a substantially horizontal position, but the useful apparatus is not limited to such an arrangement. The plane of the disc may be vertical or at an angle.

An important part of the novelty in the method of the present invention resides in this demonstration that an electrolyte having suflicient degree of solubility for metal oxides can be deposited, practically rigidized in streamline, non-turbulent flow on a rotating disc, and that a metal or other electrically conducting article brought into the outermost layer of this electrolyte can be made anodic with direct current at low voltage and much higher-than usual current'density known in the art as a result of which highly 'eifective and efficient electrolytic grinding can be done at rates at least equal to and usually exceeding the rates of electrolytically assisted abrasive methods, electric discharge methods, and of conventional abrasive methods. 1 v Since no metal removal occurs until the article to be ground contacts the electrolyte film, easy and simple operation results. Since the right gap is adjusted by metering the electrolyte film, the article is automatically spaced correctly when electrolysis current flows since no action can occur until the electrolyte is contacted upon advancing the article toward the electrolyte.

Although a rotating cathode disc having a fiat surface radially from center to outer rim can be used in performing the method of this invention, the preferred apparatus utilizes a rotating cathode disc that is concave at the center. The preferred concavity is provided with 0.002 to 0.100 inch thinner in section at the center than at the outer rim of the grinding face, decreasing radially in "a straight line tozero at the outer rim or with a 5 to 40 This concavity adds a component of centrifugal force in a better manner to impact the electrolyte against the disc surface. By the means provided according to Fig. 1 and described hereinbefore, non-turbulent electrolyte films can be easily maintained in thicknesses less than 0.008 inch. .At a given applied voltage, theamperage that can pass is greater per unit of area the thinner the electroylte film and thus the closer the article is to, but not, touching the cathode disc.

ELECTROLYTE COMPOSITIONS The following are various electrolyte compositions useful in carrying out the present .invention. They will be referred to more particularly later in this description and are here set forth together for ready comparison.

"For tungsten carbide: G./l.

Sodium tartrate (-Na C H O 1S0 Sodium hydroxide (NaOH) I50 .Sodium chloride (NaCl) 20 For composite articles:

A. Triethanolamine (HOCH CH N 1'97 Sodium hydroxide (NaOH) 50 Sodium chloride (NaCl) Sodium cyanide (NaCN) .25 Sodium. carbonate (Na CO .25

"B. Sodium tart'rate (Na C H o ,.l0'5 Sodium hydroxide (NaOH) 60 Sodium chloride (NaCl) .50 Sodium cyanidetNaCN) 25 C. 'Sodium tartrate (Na C I-I O .168 Sodium hydroxide (NaOH) 60 Sodium chloride (NaCl) 50 For vanadium steel:

Sodium chloride ('NaCl) 200 ,Boric acid P1 '25 pH? or higher preferred range 1i8'-10'or'higher.

Electrolyte compositions for carrying out the process definedherein have the chemical ability to dissolve the oxides of the metals and the metallic elements being processed Forexample, electrolytically grinding a part consisting of cemented tungsten carbide, silversolder and tool steel requiresthat tungsten oxide, cobalt oxide, silver oxide and iron oxides be dissolved. Tungsten oxide is well-known to be soluble in alkaline solutions and in soluble in acid solutions. Cobalt oxide andiron oxide are insoluble in alkaline solutions andare soluble in acid solutions. Oxides of all three metals are insoluble in neutral solutions. In electrolytes of this invention, the oxides of all the metals named are soluble because special improvements are present in an alkaline solution. The electrolyte of Example B contains sodium hydroxide'to dissolve the tungsten electrolytically, sodium tartrate to make the cobalt soluble and sodium tartrate plus sodium chloride to make the iron soluble. The sodium cyanide i'n 'this exampleprovides solubility for silver solder when the operating voltage is highenough to cause polarization of the silver. When the operating voltage is low enough to avoid polarization, the cyanide is not needed and the electrolyte of the composition Cwill electrolytically carry out the process described for a combination of the three metallic components. r

For metallic elements that are substantially steel with minor alloying constituents, chloride solutions provide suflicient solubility for the oxides and are, therefore, use ful for electrolytic grinding as described herein.

Or, in the case of an alloy, the electrolyte can be se lected for dissolving characteristics of the major con stituent and by dissolving it permit the alloying elements to fall free without need for electrolytic solubility or mechanical scraping.

In the absence of the oxidizing elfect of the electric current passed through the metallic components as anodes, these electrolytes are without substantial attack upon the metallic components. With the passage of the electric current as described herein, the metallic components are dissolved at substantial current eiliciencies according to Faradays 'law. While the operations are technically feasible at any current efiiciency for metal dissolution, we prefer to operate at values above 40% current efficiency. The balance of the electro process which makes the current efficiency total to 100 is believed to be consumed in dissociating water with the discharge of oxygen simultaneously with the metal dissolution that brings about the electrolytic grinding. For the most practical operations, current efiiciencies will exceed 80% for metal dissolution. d Generally, electrolytic processes have limiting current densities, such that increase in current density beyond this point elfects no further increase in the rate of metal dissolution. This condition is reached when the rate of metal dissolution just equals the rate at which the dissolved metal ion can be accepted by the solubilizing ions and the product can diffuse away while at the same time new acceptor ions can diffuse to the metal surface. This limiting current density condition involves a diffusion layer at the anode surface that has a thickness in the range of about 0.005 inch. The only way to speed up the anodic dissolution is to exceed the lirnting current density by disturbing the naturally-forming diffusion layer so that the products of dissolution are swept away and fresh dissolving solution is supplied at a rate faster than normal diffusion can maintain. Thus, by flowing electrolyte underforced pressure into the gap between the two electrodes, the products of dissolution are swept out and fresh solution is supplied at the high rate necessary for maintaining high-speed anodic dissolution. Thus, there is a minimum speed of freshflow in the gap between the electrodes that will correspond with or be greater than the normal difiusion film thickness. There can be an excessive amount of turbulence at the metal surface such that the diffusion film is broken up into globules of liquid and Example I Cemented tungsten carbide was plunge ground electrolytically inthe following aqueous electrolyte:

. G./1. Sodium tartrate (Na C H O 150 Sodium hydroxide (NaOH) 150- Sodium chloride(NaCl) 20 The cutting rate in inch per minute as shown in Fig. 5 was substantially directly proportional to the anode (the article being ground) current density, which also was: substantially indirectly proportional to the anode-tocathode spacing which is the effective thickness of electrolyte film. These linear relationships areto be expected only if electrode polarizations are zero or nearly zero at the cathode (rotating disc) and the anode (the article being ground). The dotted line shows the theoretical cutting rate at percent coulombic efiicienc-y. At current density above 1000 amperes per square inch, the actual efiiciency appears slightly less than 100 percent, indicating that some polarization did occur; but even so, the high coulombic anode efiiciencies shown by this example have not .heretofore been attained at current densities over a few hundred amperes persquare foot, thus attesting to a novel accomplishment by the present invention.

1 The importance ofestablishing very high current density is shown by the appearance of the carbide surface at several levels of the current density range covered by Fig. 5.

Current Density square inch) 0 to 325--.- Dull, gray anode film; uneven surface. 326 to 50 Shiny surface, but uneven.

Good edges and smooth surface (5.5 to 7.5 R.M. S. microinches 1,151 to 1,600 Good edges, but less smooth than surface at 501 .to 1,150 amp/sq. in.

For some applications, very sharp edges are desired such as those resulting from diamond-wheel grinding to sharpen cutting tools. The very high current densities. shown in Fig. 5 for Example I can only occur because cathode polarization is essentially eliminated because the high rate of electrolyte flow through the cutting gap sweeps away the hydrogen (principal product at the oathode disc surface) at the instant it forms. The slight fall off in efiiciency at the high current density end of the range shown in Fig. 5 indicates that some anode polarization may have occurred. Clearly also at the 25-volt operation, polarization at the edges was slightly less than at the rest of the surface being dissolved, so some edge rounding occurred. This is desirable for the smooth run-' ning of some engine and other mechanism parts, but is not desirable when a very sharp edge is desired as in sharpening a cutting tool.

Since the agitation for anodic dissolution in the electrolysis gap clearly reached heretofore unheard-of agitation rate by streamline flow, permitting exceptionally high current densities, electrolysis at some lower voltage should take place so that a slight decrease in agitation should cause a relatively large decrease in current density, and thus a large decrease in metal-removal rate. Because of the firmness of the electrolyte film on the cathode disc, there is no pile-up of electrolyte on the leadinge'dge V of the article being ground.v Thus, in the absence of turbulence, the. agitation effect is slightly less onapart of the article not substantially parallel to electrolyte. new.- This slight difference in agitation at an edge is'not enough to. cause the decreased current. density resulting from less agitation to offset. the greater current at edges caused by normal current distribution at 25 volts'. In the electrolyte film, as provided by the present method, it was. found. that at volts direct current, the. slightly less agitation at. the edges caused lesser current density that offset the increase. that configuration would give. current distribution to effect greater current density and metal removal at edges. So with conditions the same as for Example I except at 5 volts applied the edges were as sharp-asthose produced by diamond-wheel grinding.

The process described herein for electrolytic grinding is eminently suitable for grinding materials other than cemented carbide. Since the'process does not remove metal by mechanically cutting it away, hardness is no factor in electrolytic grinding. Thus, metals of widely different hardness can be electrolytically ground simultaneously; for example, cemented tungsten carbide, silver solder, and tool steel. Such a combination now requires tedious and careful grinding with diamond wheels and with wheels of less costly abrasives. Care must be taken not to grind silver solder and steel with the diamond wheels, and the wheel of other abrasives used to cut the silver solder and steel is worn excessively if it contacts the. cemented tungsten carbide.

. Example ll Since it is not practical to use a diamond wheel or an abrasive wheelof other type. for the complete grinding andshaping of cemented tungsten carbide, silver solder and tool steel, a method for grinding all three at once is. both novel and practical. All three metals were simultaneously electrolytically ground in thin-film electrolytes of the followingcomposition in the electrolytic grinding unit shown in Fig. 1.

A. Triethanolamine ([H0CH2CH2]3N) g./l 191 Sodium hydroxide (NaOH) g./l 50 Sodium chloride (NaCl) g./l 100 Sodium cyanide (NaCN) -L g./l 25 Sodium carbonate (Na CO -g./l- 25' B... Sodium tartrate (Na C H O -Qgl/L- 1'05 Sodium hydroxide (NaOH) g./l 60' Sodium chloride (NaCl) g./l 50 Sodium cyanide (NaCN) g./l 25 urrent density amp-./sq. in 300 Cathode wheel speed ft./min 6000 Anode area- 'sq. in 0.2 Anode to-cathode space in 0.002

Both electrolytes gave approximately the same results for electrolytic grinding at 25 volts. Cutting rate was 0.020rinch per minute; the carbide surface was smooth (5. to R.M.S. microinches), but was slightly wavy and the edges were slightly round; and the steel had a surface finish of 70 to 100 microinches.

Electrolytic grinding at 5 volts produced a flat, non wavy tungsten carbide surface with sharp edges and a smooth. polished" finish on the steel and silver solder.

The electrolyte flow system and rotating disc remain the same for presenting a thin, electrolyte film to the article to be ground. Because the electrodereactionof difierent metals diifers at high currentv densities, and the solubilities of metal oxides and salts differ, the best electrolytic grinding results will require some changes in electrolyte for difiiereut metals. Note that electrolytes A and. B of Example II differ in composition from the electrolyte of Example I. The cyanide in A and B effects dissolution of, the silver solder and the chloride prevents anodic polarization ofthesteel, solubilization ofwhich in alkaline solution ispefiected by the triethanolamine orthe tartrate,

I G./l.' Sodium tartrate (Na C H O i681 Sodium hydroxide (NaOH) 60. Sodium chloride (NaCl) .4 50

At 300 amperes per square inch, 6000 feet per minute;

disc speed, and lowest electrolyte flow that'gave unifornr' film, metal-removal. rate was0.020 inch per minute and surface finish was 10 R.M.S. microinches on boththe stock and the cemented. tungsten carbide. At the low voltage; of 5 volts the throwing power of the electrolyte is less: than at. 25 volts, so edges. are. sharper. r The electrolytes shown in Examples I and II are, for electrolytic grinding of the. grade of carbide containing 6' percent cobalt.v The concentrations. of tartrate, hy droxide andchloride in the. electrolyte will vary somewhat. as the percent cobalt is different or as nickel or other cementing metals are used.

The cation is not a factor in the process describedherein and may be any other that forms very soluble tartrates such as potassium and ammonium. In place of: tartrate, any of the following may be used: triethanol-. amine, citrate, tetrasodium ethylene diamine tctraacetatc, ammonium hydroxide, etc.

Example III High carbon vanadium steel was also electrolytically ground at high rates by the method of thisinvention An electrolyte consisting of an aqueous solution, of 200 g./l. sodium chloride and 2-5 g./l. boric acid was used. At cathode disc speed of 6000 feet per minute, 25 volts applied E.M.F., cutting rates of 0.010 to 0.140 inch per, minute were attained depending on the anode-to-cathode v gap (i.e., the electrolyte film thickness) as shown in Fig.- 6.- Projection of the line for anode-to-cathode spacing". shows an electrolytic cutting rate of about 0.165 inch'per: minute at 0.001 inch spacing. Low-alloy steels, high and low carbon steels, and stainless steels can be electrolytically ground under the conditions cited for Example III. Cutting rates are substan-' tially the same for all. Very little difference-is seen in cutting rates as pH varies from 1.8 to 10. Finish ap; pearance is slightly better at pH of 7 andhighcr. At 5 volts, electrolytic cutting rate is slightlyslower than at 25 volts, but surface finish is better for some metals. Thus, a roughing. cut can be taken at the higher voltage for speed and finishing can be done for appear ance at the low voltage. The only change is in voltage regulation, whereas, for abrasive wheel grindingeither the wheel must be changed or the work must be reset-up on a second machine for finishing after roughcutting,, The aspect of variability of voltage is a characteristic of electrolytes having good conductance and high solubility for metal oxides and anodic oxidation of metal corny pounds with non-metals such as represented by tungsten carbide. Thus, a feature of the present process is the use of an electrolyte composition giving good electrical conductance and having high solubility for metal oxides and for salts of the anions in the electrolyte and the metal dissolvedduring the electrolytic grinding.

For accomplishing electrolytic grinding as disclosed herein, wheel speeds (cathode disc speed) are those at which a uniform uninterrupted smooth film of electrolyte is formed at point of discharge of the electrolyte from the circulating pump to the location behind the metering dam. Generally, wheel speeds will be in the range of 2000 to 15,000 feet per minute, depending on the viscosity-of, the. electrolyte.- More specifically, speeds of 6000 to 10,000 .feet per minute are preferred.

in general, current density on the article (as anode) to be electrolytically ground will be 100 to 2000 amperes per square inch. More specifically, 500 to 1600 amperes per 'square inch are preferred.

Electrolyte film thickness (anode-to-cathode gap) will be 0.0001 to 0.020 inch. More specifically, film thickness in the range of 0.001 to 0.008 inch are preferred, depending on the composition of electrolytic solution being used, the metal being electrolytically ground, and the voltage being used, as for rough cut or fine finishing.

Operating voltages will generally be in the range of 2 to 30 volts. More specifically, voltages of 5 to 25 volts should be used for practical electrolytic grinding rates.

The material of the cathode disc is not important so long as it has adequate electrical conductance and resistance to chemical attack in the electrolyte and is not damaged by hydrogen discharge.

Other advantages of the method of this invention will be apparent to those skilled in the art of electrolysis and of metal grinding, machining and shaping. For example, electrolytic grinding is accomplished without generation of damaging heat in the article to be ground or pressure on the article to be ground and, being in addition without physical contact, cannot introduce damaging stresses in the surface of hardened steels; cannot leave torn, fragmented, damaged metal on a surface such as results from the ripping, shearing, tearing and smearing by which abrasives and contact tools cut; cannot deform thinsection metal parts; and is not hampered by plastic flow of soft metals that fill abrasive wheels and smear under contact-cutting tools.

Throughout the preceding description reference has been made to the employment of a disc 2 as the cathode on which the electrolyte is supported and to which electrolyte film the work to be electrolytically formed is presented. In Fig. 4 there is shown an alternative arrangement wherein a rotating spindle 30 carries a disc 31 having a substantially cylindrical flange 32 integral therewith. The electrolyte is introduced through conduit 34 and distributed by the dam or baflie 35 on the end of the conduit. 'The Work piece to be electrolytically formed is indicated generally at 36 and is held by a suitable arm 37 by which it may be presented to the electrolyte film in the manner previously described in connection with Figs. 1, 2 and 3.

ADJUSTMENT OF ANODE-CATHODE SPACING One simple means by which this can be accomplished is illustrated in Fig. 7 wherein 40 designates the direct current control circuit power source, 41 is a rheostat for the control of the speed of a variable speed reversing motor 42, the direction of rotation of which is controlled by the reversing switch 43. The shaft of the motor 42 is connected through a gear box 44 to a gear 45 on the adjusting stem 46 of the universal vise 47, the arm 48 of which carries the work piece 49 in the proper spaced relation to the disc 50. 51 denotes the DC. power source for the work circuit, 52 is the rheostat by which that circuit is controlled and 53 is the switch by means of which the circuit is energized and de-energized.

Electrolytic grinding withoutthe arcing, sparking or scraping as in the prior art is inherently self-adjusting. If the feed rate tends to exceed the cutting rate, the gap will decrease, causing the current density to increase, and the cutting rate will increase to a value equal to the feed rate. Conversely, if the cutting rate tends to exceed the feed rate, the gap will increase causing the current density to decrease, and the cutting rate will decrease to a value equal to the feed.

Anode feed can be accomplished by the variable speed motor 42 with the gear reduction train 44 to allow feed rates covering the range of cutting rates achieved in electrolytic machining (i.e., 0 to 0.2 inch or more per minute). The reversing switch 43. is provided to with-.

. draw the work 49 from the cathode disc 50 when the shown in Fig. 7, a separate switch 53 is provided for the electrolysis grinding circuit. Alternatively, the reversing switch mechanism couldbe arranged to simultaneously.

open or close the electrolysis grinding circuit.

There are several methods of terminating the cutting action after the desired amount of metal removal. The choice will depend on the requirements of the machining operation. The following examples illustrate the unique control features possible for electrolytic machining with present-anode-feed-rate control:

(1) Cutting action can be terminated by an adjustable limit switch which is mechanically activated by the anode feed holder. The limit switch would simultaneously open the electrolysis circuit and reverse the feed direction. The advantage of this method is that the limit switch can be set with reference to the cathode disc. No further adjustment of the limit switch setting would be required in repetitive machining operations, since there is no wear on the cathode disc. In conventional machining or other electrolytic processes, tool wear or cathode-disc wear'must be continually compensated by some means in order to achieve reproducible accuracy.

(2) An electric timer could be set in conjunction with the preselected feed rate, so as to terminate the cutting action after the desired anode feed travel from the initial position. At the end of a specified time, the electric timer can activate the mechanism for opening of the electrolysis circuit and reversing of the feed direction.

(3) Similar to 2, except that the start of the electric timer would be activated by the start of the electrolysis current. In this manner, the timing of the depth of cut can be started when the anode entered the electrolyte. The advantage of this method is that by suitable choice of time and feed rate, a definite depth of out can be obtained independent of the initial positioning of the anode in the holder.

(4) For'precision work on a production basis of a number of similar parts of known anode area, an ampereminute meter connected in the electrolysis circuit will control and limit the electrolytic grinding. The cutting action can be terminated after a predetermined number of ampere minutes of electricity have passed. As an example, assume an anode area of 0.1 square inch and a cutting rate of about 0.050 inch per minute at 1000 amperes per square inch. In cutting 0.050 inch, ampere minutes will pass. With an ampere-minute meter sensitive to the nearest tenth of an ampere minute, the precision of cut will be 0.00005 inch.

In operation, the desired anode-feed rate and electrolysis voltage are selected. The electrolysis circuit is closed, and the anode feed toward the cathode disc is begun. As the work enters the electrolyte, current flows, and metal removal begins. At the gap distance set, the cutting rate will be less than the anode-feed rate; therefore, the gap will tend to decrease, the current density will increase, and the cutting rate will'increase, untilthe cutting rate equals the feed rate.

It is also contemplated to provide a voltage-control unit. This consists of a voltage divider to select from the line voltage the desired electrolysis voltage. During electrolysis, the equilibrium gap spacing that exists when the feed rate equals the cutting rate can be controlled by the electrolysis voltage. The gap for electrolytic grinding, as described herein, is directly proportional to the electrolysis voltage. The electrolysis voltage is selected so that the equilibrium gap distance is less than the electrolyte film thickness on the cathode disc, but large enough to prevent arcing or sparking. ,Figure, 8 shows the general relationship betweencur- 115 test density, cutting rate and gap spacing at various voltages, as characteristic of, electrolytic ma in n as described. herein. The exact numeral values and relation ships will depend on many factors, i.e.', the type of anode material, the electrolyte, etc. In Fig. 8, a straight-line relationship between gap distance andcurrent density is shown forsim-plicity. The important factor is that the current density is inversely proportional; to the gap spacing for the purposes of gap control during electrolytic machining. A straight-line relationship is not essential.

This control system, based on a preselected cutting rate, isadvantageous because the method is independent of. the anode area beingrmachined. This control system does notrequire. auxiliary electronic equipment. It is apparent that sucha simple control system can only be used for electrolytic machining without scraping, sparks ing or arcing. Such a control system would not be-feasi'olc if continual contact of the anode and cathode were required during electrolysis.

in Figs. 9 and are shown modes for electronically controlling the gap or spacing between the anode and cathode when the thickness of the electrolyte film on the cathode is at least as great as such spacing.

'l-he purpose of this electronic equipment isto provide an automatic control of the gap between the tool and the, cathode disc. When machining surfaces of essentially constant areas using a constant voltage source, the electrolytic current flowing is a measure of the gap between the tooland the disc. This phenomena is used as a basis of control in the circuit shown in Fig. 9. I WhenSWl is closed, current from the power mains flows through thev primary PI of transformer X1. Voltage induced'in secondary 1 is applied to the filaments of tubes V V2, V and V causing them to heat, and activates the metalreed of converter CON-1. Voltage inducedin SEC 2 is applied between the right hand plate of V and bus 8-1 by means of wires A and B. The right hand section of V is connected as. a rectifier and a D.C. voltage is caused to appear between-terminals T mar, T is positive in polarity with respect to T Resistor R and capacitor C are part of a filtering network which smooth the fluctuations from the rectified DC. voltage. In the phase sensitive amplifier, R R and R are bias resistors placed in the cathode circuits of V V and V; respectively. C and C, are cathode by-pass capacitors to reduce degeneration. C and'C are decoupling capacitors.

vIn the electrolysis circuit, current 1 flows from the voltage source E through wire C to the wheel by means of a brush. The current then passes through the gap between the wheel and the work by means of an electrolyte, removing material from the work. Said current then passes from the specimen back to the source E by means of wire D and resistor R and wire E. A voltage 1;, is developed across resistor R between terminals T3 and T by thepassageof the electrolysis current. The magnitude of this current and voltage v will depend upon the area of the specimen and the size of the gap betweenrthe'wheel. and the specimen. In the reference voltage circuit, current I passes from the source E through resistors. R R and R and back to the source E This current 1 is controlled in magnitude by fixed resistors fRg and R and variable resistor'R R is present to control the maximum of current which flows when R is at a minimum. In operation, R is adjusted so that the proper current I flows through R establishing a voltage v between terminals '1, and T equal to v, etwee n terminals T and T when the desired amount of electrolysis current is flowing. When the desired aniount'of electrolysis current is flowing, v is equal to v,. The polarities of v and v are so arranged that when v and V; are equal in magnitude, no net voltage appears between terminals T and T Converter 1 operates in conjunction with transformer x inisucha manner that a 60 cycle alternating voltage transmitted through wires F and G, through reversing switch (SW-3 to terminals T and T thence by wires H and I to converter CON-1. Since the voltage between T and T is zero, the voltage v that appears between terminals T and T is also zero. When there is no voltage at T the grid G of the left hand section of tubal is at the same potential as cathode K This lets the left hand section of tube V pass current. These electrons flow from bus B1 through R through the left section of tube V R R and R to terminal T A voltage v appears across R which is positive at K and negative at B 1. This makes cathode K more positive than grid G decreasing the current in the left hand side of tube V This voltage 1 across R is the grid bias of the left hand side of tube V Hence, with no grid signal, the left hand side of V passes a small steady current, producing also a voltage drop across R R and R However, no matter what steady voltage appears between points T and T capacitor C charges to this voltage, and no voltage remains across resistor R Similarly the anode current which passes through the right hand side of tube V; develops a voltage across R which is a biasing voltage. This limits the anode current in the right hand side of tube V, to a small steady flow. This has no effect on the left hand side of Y for capacitor C has charged to the voltage between points T and bus B-ll, so that no voltage remains across R The left hand side of V also has zero grid voltage and passes some anode current. Similarly, C; has charged to the voltage T to bus B-1, and grids G G G and G of both tube V and V, are at the. same potential as bus B-l.

Although in all sections of V and V the cathodes are tied together, and the grids are tied together, the tubes are not in parallel. Anodes P and P are connected by wire I to terminal T one side-of transformer X secondary 3. Anodes P and P are connected by wire K to terminal T the other side of secondary 3 of transformer X The left hand section of V and the right hand section of V may fire during one half cycle. The right hand section of V and the left hand section of V may fire during the next half cycle. Never do all four sections of V and V pass current at the same time. While their grids, attached to terminal T remain at B-l potential, tubes V and V act as a two tube full wave rectifier, producing a small direct current. Theseelectrons flow from terminal T the center tap of SEC. 3, transformer X1 through wire'L, through one set of windings (W-l) in the two-phase motor, through wire M to bus B.1, through R, to cathodes K K K and K and throughthe left and right sections of V and V; in turn. The voltage developed across R makes cathodesK K3 K and K more positive than grids G G G and G attached to terminal T thus acting as grid bias. This limits the amount of anodecurrent of V 3 and V This directcurrent through the. motor windings does not turn the motor, which is an AC. induction motor, but tends to make it more stable. So, until a signal voltage appears at T all tubes'pass current steadily but the motor does not turn.

in Fig. 9, suppose that the electrolysis current I decreases, lowering the voltage v developed across R to a value less than 1 developed across R A voltage thus appears between terminals T and T which is positive at T and negative at T Withrswitch SW-3 in the down position this voltage appears between terminals T 6 and T and is carried by wires H and I to the converter CON-1. Consequently a 60 cycle signal voltage appears at T as shown in curve 2, Fig. 10. During the half wave X, grid G becomes more positive, increasing the anode current of the left hand section of V This reduces the potential at terminal T Since capacitor C cannot change its charge instantly, the potential at G is forced more negative. Since the grid voltage of the right hand side of V becomes negative, its anode current decreases. When the current decreases in the right hand side of V the potential at terminal T increases. Since capacitor C cannot change its charge instantly, the potential at terminal T also increases. When the potential at terminal T increases, the anode current through the left hand side of V increases, decreasing the potential at terminals T and T The slider on resistor R is a sensitivity control. When it is moved toward the lower end, less of the voltage developed across R is used to change the current in the left hand side of V so the whole amplifier has less output at terminal T During the half wave X when current increases in the left hand side of V decreases in the right hand side of V and increases in the left hand side of V the potential at terminal T decreases. Coupled through capacitor C the potential at terminal T is more negative than bus B-l. Curve 3 of Fig. shows this change at T which is the grid voltage of tubes V and V During half cycle X, anodes P and P are positive, and anodes P and P are negative. No tube section passes current since the voltage of all grids of tubes V and V is negative. However, during the next half cycle, all the grids of V and V, are positive. Although all grids are positive, only the left hand section of V and the right hand section of V, will pass current, for P and P are now negative. The amount of this current increases if the voltage signal (curve 2, Fig. 10) becomes larger.

From the above we see that the left hand section of V and the right hand section of V pass half cycle pulses of current whenever voltage -v is less than voltage v These current pulses (curve 4, Fig. 10) are changed into an alternating current by adding capacitor C which is the proper size to resonate at 60 cycles with the motor windings W1. Current flows back and forth through windings W-1 and in and out of capacitor C This current is started and kept flowing by the pulses of current (curve 4, Fig. 10) from the left hand section of V and the right hand section of V Since the current lags by 90 when flowing through an inductive coil, the current wave form through coil W-l will lag by 90 (curve 5) the pulses of current from the left side of V and the right side of V The two phase motor requires an alternating current in each winding. When switch SW-Z is closed, SW-l having been closed, 60 cycle current flows from the mains through wire 0, motor windings W-Z, wire-N, switch SW-2 and capacitor C back to the mains. Since the current in an inductive coil lags the applied voltage, capacitor C is added to bring the current wave form in the coil (curve 6, Fig. 10) more nearly in phase with the applied voltage.

When the left side of V and the right side of V alone pass current, the current in the motor W-1 windings is shown by curve 5. This is also shown in curve 7, which includes curve 6 (current in the W-2 windings). The

W-l winding current is to the left of the W-2. winding current and leads by 90 degrees (curve 7, Fig. 10). These combined currents make this induction motor turn so as to move the specimen holder toward the cathode wheel, decreasing the gap and increasing the current I When the current 1 increases, so that voltage v is larger than voltage v there will again be a voltage be tween terminals T and T However, this voltage will have a polarity opposite that which occurred in the previous discussion. When this signal voltage is applied to 18 converter CON-1 the resultant 60 cycle signal at terminal T is like curve 9, "Fig; 10, or shifted 180 degrees from the previous signal as shown in curve 2, Fig. 10. Since T is negative during the first half cycle, the current in the left hand side of V decreases, the current in'the right hand side of V increases, the current in the left hand side of V decreases, and the signal at terminal T 17 becomes more positive, as shown in curve 10. During half Wave Z, the grids of tubes V and V, are all positive. However, the anodes P and P are negative during this half cycle and the left hand section of V and the right hand section of V, will not pass current. Anodes P and P are positive during this half cycle so the left hand section of V and the right hand section of V may pass pulses of current (curve 11, Fig. 10 These pulses cause an alternating current to flow in winding W-1 of the motor and resonating capacitor C This alternating current curve (curve 12, Fig. 10) lags degrees behind" the wave of current through the left section of V and the right section of V (curve 11, Fig. 10). Since these tube currents (curvell) occur a half cycle later than currents illustrated in curve 4, the wave of current in the W-1 windings is also later. In the combined curves 14 we see that the W4 winding current is to the right of the W-2 winding current, and lags by 90 degrees. combined currents make the induction motor turn was to retract the specimen from the wheel and cause the gap to increase and decrease the current.

Thus, by tapping 01f a voltage developed by the electrolysis current, it is possible to control the gap present between the specimen and the cathode wheel. The twophase motor responds immediately and accurately to keep the current and gap constant.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

We, therefore, particularly point out and distinctly claim as our invention:

l. The method of sharpening, shaping and finishing an electrically conductive body by removing stock therefrom, which comprises metering a thin layer of electrolyte said body in contact with the electrolyte film but spaced from the conducting surface supporting the same during such stock removal operation.

2. The method of sharpening, shaping and finishing a metallic body by removing stock therefrom, which comprises metering a thin layer of electrolyte onto a smooth electrically conducting surface moving at high speed to form a conductively supported film of the electrolyte of a thickness within the range of from about 0.001 to about 0.008 inch moving rapidly in streaml ne,

non-turbulent flow, thereafter disposing the surface of said body from which stock is to be removed in contact with the thus preformed film of electrolyte, applying direct current voltage across the body as an, anode and the conducting film-supporting surface as a cathode, to

remove stock from the body, said electrolyte having high solubility for the metal oxides produced by the electrolytic dissolution, and maintaining such surface of said body in contact with the electrolyte film butspaced from the conducting surface supporting the same during such stock removal operation.

These 3"; The method of sharpening, shaping and finishing an electrically conductive body by removing stock therefrom, which 'comprises'metering a thin layer of electrolyte onto a smooth electrically conducting surface moving at high speed to form a conductively supported film of the electrolyte of a thickness within the range of from about 0.001 to about 0.008 inch moving rapidly in streamline, non-turbulent flow, thereafter disposing the surface of said body from which stock is to be removed in contact with the thus preformed film of electrolyte, applying direct current voltage across the body as an anode and a conductive film-supporting surface as a cathode to remove stock from the body, and advancing the body during such stock removal operation at a predetermined uniform rate of feed, such surface of said body being maintained in contact with the film of electrolyte but spaced from the conducting surface supporting the same.

4'. The method of sharpening, shaping and finishing a metallic body by removing stock therefrom, which comprises metering a, thin layer of electrolyte, having high solubility for the metal oxides produced by the electrolytic dissolution, onto a smooth electrically conducting surface moving at high speed to form a conductively supported film of the electrolyte of a thickness within the range of from about 0.001 to about 0.008 inch moving rapidly in streamline, non-turbulent flow, thereafter disposing the surface of said body from which stock is to be removed in contact with the thus preformed film of electrolyte, applying'direct current voltage across the body as an anode and the conductive film-supporting surface as a cathode to remove stock from the body, and advancing the body during such stock removal operation. at a predetermined uniform rate of feed, such surface of said body being maintained in contact with the film of electrolyte but spaced from the conducting surface supporting the same.

5 The method of sharpening, shaping and finishing a. metallic body by removing stock therefrom, which comprises metering a thin film of electrolyte, in which the metallic oxides produced in the electrolytic dissolution, of said body are soluble, onto a smooth rapidly moving electrically conductive surface in streamline, nonturbulent flow, the thickness of said film of electrolyte being within the range of from about 0.001 to about 0.008 inch, thereafter disposing the surface of said body from which stock is to be removed in contact with the thus preformed film of electrolyte, applying direct current voltage across the body as an anode and the conductivefilm-supporting surface as a cathode to remove stock from the body, and advancing the body during such stock removal operation at a predetermined uniform rateof feed, such surface of said body being maintained in contact with the film of electrolyte but spaced from the conductive surface supporting the same.

6. The method of sharpening, shaping and finishing a metallic carbide body including metallic cementing material, by electrolytically removing stock therefrom, with out formation thereon of a solid polarizing film of oxide, which comprises discharging an electrolyte in which the oxides of the carbide and the metallic cement of said body are soluble onto a smooth rapidly moving electrically conductive surface, such discharge being metered to form a thin non-turbulent film of the electrolyte of a thickness within the range of from about 0.001 to about 0.008 inch on said surface, thereafter disposing the surface of said body from which stock is to be removed in contact with the thus preformed film of electrolyte, applying direct current voltage across the body as an anode and the conductive film-supporting surface as a cathode to. remove stock from the body, and maintaining such surface of said body in contact with the electrolyte film but spaced from the conductive surface supporting the same during such stock removal operation.

. 7. The method of sharpening, shaping and finishing a cobalt-cemented tungsten carbide body by electrolyti-- cally removing stock therefrom, without formation theredischarging an'el'ectrolyte in which tungsten oxides are soluble. and which contains a cobalti solubilizing grouponto 'a smooth rapidly moving electrically conductive surface,'s uch discharge being metered to form a thin nonturbulent film of the electrolyte of'a thickness within the range of from about 0.001 to about 0.008 inch on said surface, thereafter disposing the surface of the body from which stock is to be removed in contact with. the thus preformed film of. electrolyte, applying direct current voltage across the body as an anode and the conductive film-supporting surface. as a cathode to remove stock from the body, and advancing the body during such stock removal operation at a predetermined uniform rate of feed, such surface of said body being maintained in contact with the film of electrolyte. but spaced from the conductin g surface supporting the same.

8. The method of electrolytically sharpening, shaping and finishing simultaneously all. three components. ofv a composite workpiece in which cobalt-cemented tungsten carbide is brazed to a steel body, without formation of a polarizing film of oxide, which comprises discharging an alkaline cyanide-amine chloride electrolyte onto a smooth rapidly moving electrically conductive surface, such dis charge being metered to form. a thin non-turbulent film of the electrolyte of a thickness within the range of from about 0.001 to about 0.008- inch on said surface, thereafter disposing the surface of said workpiece from which stock is to be removed in contact with the thus preformed film of electrolyte, applying direct current voltage across the workpiece as an anodeand a conductive film-supporting surface as a cathode toremove stock from the workpiece, and maintaining such surface of the workpiece in contact with the electrolyte film but spaced from the conductive surface supporting the same during such stock removal operation.

9. The method of sharpening an. electrically conductive body by electrolytically removing stock from a selected surface of said body to produce a sharp edge thereon, which comprises metering a thin layer of electrolyte onto a smooth electrically conductive surface, while moving such surface at high speed to form thereon a conductively supported film of the electrolyte of a thickness within the range of from about 0.001 to about 0.008 inch moving rapidly in streamline, non-turbulent flow, thereafter disposing the surface of said body from which stock is to be removed in contact with the thus preformed film of electrolyte, with the edge of the selected surface to be sharpened facing upstream and substantially at right angles to the direction of movement of the film of electrolyte, applying direct current voltage across the body as an. anode and the conductive film-supporting surface as a cathode to remove stock from such selected surface of the body, and maintaining such surface of the body in contact with the electrolyte film but spaced from the conductive surface supporting the same during such stock removal. operation.

10. Apparatus for sharpening, shaping and finishing conductive bodies electrolytically, comprising a rotatable cathode disc having a smoothly dished surface, an electrolyte delivery conduit having its discharge opening closely spaced adjacent such surface of the cathode disc, baffle means at such discharge opening of the delivery conduit arranged generally transversely thereof and having a bottom margin in close-spaced relation to such surface, whereby electrolyte. flowing from such opening is deflected by said baffle means under such bottom margin thereof and deposited on the cathode surface, upon rotation of the same, as a' thin. layer, drive means for rotating the cathode disc at high speed thereby to impact the electrolyte thereag-ainst by centrifugal force and form a thin, rigidized' film of electrolyte on such surface, support means spaced from and independent of said baflle meansfor mounting a conductive workpiece in contact with said film of electrolyte, and means for applying electrolysis voltage across said cathode and said workpiece as an anode.

11. Apparatus for sharpening, shaping and finishing conductive bodies electrolytically, comprising a rotatable cathode disc having a smooth surface, an electrolyte delivery conduit having its discharg opening closely spaced adjacent such surface of the cathode disc, baifie means at such discharge opening of the conduit arranged generally transversely thereof and having a bottom margin in close-spaced relation to such surface, whereby electrolyte flowing from such opening is deflected by said bafiie means under said bottom margin thereof and deposited on the cathode surface, upon rotation of the same, as a thin layer, drive means for rotating the cathode at high speed to form a thin, non-turbulent film of the electrolyte on such surface, support means spaced from and independent of said bafiie means for mounting a conductive workpiece in contact with said film of electrolyte, and means for applying electrolysis voltage across said cathode and said workpiece as an anode.

12. Apparatus for sharpening, shaping and finishing conductive bodies electrolytically, comprising a cathode having a smooth surface, electrolyte delivery means so constructed and located adjacent the cathode as to discharge electrolyte on such cathode surface with negligible turbulence in a thin wide stream, means supporting said cathode for movement relative to said electrolyte delivery means, drive means for thus relatively moving said cathode at high speed, thereby to form a thin non-turbulent film of the electrolyte on the smooth cathode surface, support means spaced from and independent of the electrolyte delivery means for mounting a conductive workpiece in contact with the thus formed film of electrolyte, and means for applying electrolysis voltage across said cathode and said workpiece as an anode.

References Cited in the tile of this patent UNITED STATES PATENTS 2,739,935 Kohl et a1 Mar. 27, 1956 2,741,594 Bowersett Apr. 10, 1956 2,767,137 Evers Oct. 16, 1956 2,798,846 Comstock July 9, 1957 2,826,540 Keeleric Mar. 11, 1958 2,827,427 Barry et a1 Mar. 18, 1958 OTHER REFERENCES Steel, vol. 130, No. 3, Mar. 17, 1952, pp. 84-86, by Keeleric. 

1. THE METHOD OF SHARPENING, SHAPING AND FINISHING AN ELECTRICALLY CONDUCTIVE BODY BY REMOVING STOCK THEREFROM, WHICH COMPRISES METERING A THIN LAYER OF ELECTROLYTE ONTO A SMOOTH ELECTRICALLY CONDUCTING SURFACE MOVING AT HIGH SPEED TO FORM A CONDUCTIVELY SUPPORTED FILM OF THE ELECTROLYTE WITHIN THE RANGE OF FROM ABOUT 0.001 TO ABOUT 0.008 INCH MOVING RAPIDLY IN STREAMLINE, NON-TURBULENT FLOW, THEREAFTER DISPOSING THE SURFACE OF SAID BODY FROM WHICH STOCK IS TO BE REMOVED IN CONTACT WITH THE THUS PREFORMED FILM OF ELECTROLYTE, APPLYING DIRECT CURRENT VOLTAGE ACROSS THE BODY AS AN ANODE AND THE CONDUCTIVE FILM-SUPPORTING SURFACE AS A CATHODE TO REMOVE STOCK FROM THE BODY, AND MAINTAINING SUCH SURFACE OF SAID BODY IN CONTACT WITH THE ELECTROLYTE FILM BUT SPACED FROM THE CONDUCTING SURFACE SUPPORTING THE SAME DURING SUCH STOCK REMOVAL OPERATION. 